Shadow culture secretary John Whittingdale has warned that the freedom of the press is under threat as a result of the government's communications bill.

In a House of Commons debate this afternoon, Mr Whittingdale will argue that giving new super regulator Ofcom a say in "public interest matters" affecting newspapers as well as ownership issues would seriously endanger the freedom of the press.

"There is a real concern that this bill, far from protecting press freedom does quite the opposite. It may be the law of unintended consequences. Or it may be something far more cynical.

"The secretary of state already possesses exceptional powers in this area. Giving an additional responsibility to Ofcom is unnecessary and potentially dangerous," Mr Whittingdale, who took over from Tim Yeo as the Tory culture spokesperson earlier this year, will argue.

He argued that it was essential that publishers were subject to no special legal regime in the interests of freedom of speech and accountability. He also pointed out that the government had repeatedly shown its support for the current system of press self-regulation.

"These are issues on which Ofcom lacks expertise, where its role is already carried out by the office of fair trading and which may have the consequence of introducing statutory legislation on newspapers through the back door."

The previously unnoticed clause was the subject of a strident leader this morning in the Daily Mail. The newspaper called on the British press to wake up to the "insidious" implications of the bill.

"In its present form, the Ofcom legislation would enable an authoritarian prime minister to introduce censorship, claiming to be acting in the public interest," it said.

"This is too important a matter to leave to chance. The current secretary of state may well give assurances that there is no intention to introduce statutory legislation of the press through the back door, but Ofcom will be an immensely powerful body that will long outlive those who are currently in charge of this bill," Mr Whittingdale will announce.